1. Field of the Invention
The invention relates to a method for curving a glass sheet, wherein the glass sheet is heated to bending temperature, is engaged in a horizontal attitude by an overhead suction device, is transported to a location above a curving-form frame which defines contour of the glass sheet, and is deposited onto the said frame, wherewith the glass sheet takes on the shape of the frame on its (the glass sheet's) perimeter, and the said frame subsequently transports the glass sheet to a cooling station.
2. Background of the Prior Art
Method of this type are described in German Pat. No. 2,945,776 and Europe A1 No. 0 003 391. The furnace in which the glass sheet is heated to bending temperature is preferably a horizontal pass-through (continuous) furnace in which the glass sheet is conveyed through the furnace while resting on rollers or on a gas cushion. A suction device which can be raised and lowered is disposed at the end of the furnace. The suction plate of the suction device is flat or slightly curved. The said plate is lowered to the heated glass sheet, which it aspirates and said plate is then raised again. A curving-form frame is then moved under the raised glass sheet. As soon as the frame is positioned under the glass sheet, the vacuum in the suction device is released, so that the glass sheet falls onto the curving-form frame, and comes to rest intimately against said frame by virtue of its (the glass sheet's) kinetic energy and weight. The curving-form frame with the glass sheet is then conveyed to a cooling station neighboring the curving station, where it is tempered (prestressed), e.g., by rapid cooling with air jets.
This known method has various drawbacks. These include, in particular, the fact that the action of gravity and/or the kinetic energy of falling on the glass sheet causes said sheet to sag in the curving-form frame in an uncontrollable fashion, so that, e.g., it is impossible to effect a purely cylindrical curvature. Further, only more or less weak curvatures can be produced, because the bending forces achievable are limited by the height of fall and the weight of the glass sheet.
The underlying problem of the present invention is to devise a curving method of the general type described initially supra, which does not result in undesired sagging in the curving-form frame, and which enables the glass sheet to be more strongly curved than is possible when relying only on the weight of the sheet or on the kinetic energy of falling of the sheet.